This invention relates to a method of monitoring a network of peripheral elements handled by an electronic control unit, and to an arrangement for applying this method, especially in telephonic switching.
The object of the method according to the invention is to solve a problem which arises in the case of a network of centrally controlled elements, comprising a central unit of the electronic computer type connected by wire to the elements of the network when the network is the centre of d.c and/or a.c voltages of a higher order of magnitude than the feed voltages of the central unit. This is particularly the case with lines of a telephone network (fed with 48 volts) switched electronically by a central unit of which the logic elements are fed with voltages of the order of 1 volt. The network and its elements in the process of operation are sources of parasitic pulses of which the transmission by connecting wires is in danger of interfering with the operation of the logic circuits of the central unit by causing the appearance of a large number of "faults" which are incompatible with the reliability of the switching system.
Accordingly, it is advisable to isolate the feed voltages of the network and the central unit from one another whilst at the same time enabling the central unit to monitor the momentary position of the elements of the network to be handled by the central control unit. In particular, precautions have to be taken to prevent the transmission of parasitic pulses by the connecting wires.
One possible solution to this problem would be to use radioelectric transmission. This would involve installing pairs of transmitters and receivers at a rate of at least one pair per element handled. When there are numerous elements, which is especially the case in a switching centre where numerous telephone lines have to be handled, the installation costs would be very high. In addition, this solution would not completely eliminate the difficulties caused by the parasitic pulses, part of whose frequency spectrum would definitely fall within the transmission channel used by certain pairs of emitters and receivers.
Another possible solution would be to install photocouplers in the monitoring lines between the "network" side and the "central" side, but conventional photocouplers are not very fast and have a relatively short service life.
The solution provided by the present invention does not have any of the disadvantages referred to above.